best way to control rotary table with stamp???

I would say a servo would work fine. But how many degrees do you need
the table to turn? If you have a regular rc servo that doesn't quite
turn 360 degrees and then gear it down 10:1, you would get even less
rotation wouldn't you? And I'm not sure about the single string design
of the stamp. In my experience it has been very easy to drive rc
servos with the stamp. If you were to get a digital rc servo you would
only have to give it one pulse to tell it want position you want it to
go to. Saving some processing power.

Joe McKibben

Hi,

Why not use a stepper motor? Hardware wise it's a normal motor and from the
CPU you just need 2 pins if you use a L297

Regards
Ian Dobson

Home of the Atmel based UDP mobile web cam http://www.planet-ian.com
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I assume you are using a R/C Servo with the idea of modifying it for
continuous rotation.  So, that gives you direction and speed control
of the motor.

Your encoder will need to have two channels, to allow for you to
detect pulses, and direction.  You will need two pins for that, and
will also need to ensure that your stamp has enough free time to
process the pulses without missing any.

I wonder if there might be a dedicated stepper/encoder setup, which
has a serial control line, and is price friendly for the hobbiest?  I
just googled, and came across this in the UK,
http://www.active-robots.com/products/motorcon/motion-mind.shtml

Anyone else have a source for something like this?

Joe Dunfee

Make one of these:

http://www.bmumford.com/rotary/index.html

It is not too hard but you will obviously need to find and mount a
stepper motor an buld a suitable driver. The results are excellent
however. A stepper will be much easier to couple than a servo and there
are no end stops.

A rotary table might have a 40:1 reduction in the worm drive and the
stepper has 400 steps per revolution giving you 360/16000 = 0.0225 deg
resolution.

Here is another one:
http://www.embeddedtronics.com/rotary.html

Pete

From a hardware standpoint I'm with Pete: use a stepper. Even with full
step, and the typical 1.8 degree step, you'll have 0.18 degrees with a
10:1 reduction. If you half step, which is easy in software, you'll get
about 0.09 degrees. BUT...the half-steps usually aren't equidistant. If
you want more accurate positioning either get a higher resolution
stepper, or go with a higher gear reducer. You can limit backlash by
going with a worm drive.

Those 15 degree steppers are probably pretty old or were pull-outs from
old equipment, but in any case, it's easy enough to find 1.8 degree
steppers surplus. Try Herbach & Rademan, C&H, the usual places.


I'd use a stepper controller chip, such as the L297, coupled to an L298
(use www.findchips.com to locate sellers of these). You control the L297
with step and direction pulses; it provides the translation. The L298 is
a power driver. The L297 is quite old but available lots of places; you
can find translator/driver chips from Allegro. The more modern chips
have at least full and half step modes, and many have wave and microstep
modes. Most are under $10, and you can sometimes get free samples.
They're not always available in DIP packaging, though.

In any case, the BASIC Stamp is perfectly suited for this task. You can
rig up an optical encoder easily as well. I'd go with the VLSI decoder
chips from US Digital -- about $3.50 each. They connect to any
quatrature encoder, and provide step and direction pulses. Makes it
very, very easy to interface to a Stamp.

-- Gordon